The present invention relates to a method of producing numerical values which are proportional to the frequency of measured pulses of a measured pulse train and to an arrangement for performing this method.
Rotational speeds can be measured by pulse generators producing pulse trains whose frequencies are proportional to the rotational speeds. An exact registering of the velocity can be attained by measuring the pulse-to-pulse period. To this end, clock pulses of an oscillator which delivers a pulse train with constant frequency are counted during the pulse-to-pulse period. When it is desired to calculate the rotational speeds on the basis of these counted values, reciprocal values will have to be formed.
There is known from the published German Application P No. 30 03 876 a method for speed determination, wherein the measured pulse of a pulse converter serves to initiate the counting of clock pulses until the number of clock pulses corresponds to a presettable time. This counting action will then be continued until the next pulse of a definable number of measured pulses occurs. The velocity sought will be determined by the ratio of the total number of the clock pulses counted to the preset number of measured pulses. According to this method, speed determination can be obtained by division only. It is often desired to sense the velocity with great accuracy. In doing so, there result figures with several digits. These figures can be divided in a relatively short time only while using extensive circuit configurations. With relatively little expenditure in circuit schemes, there ensue long calculating periods due to the sequential processing of the individual digits.
The calculating period is frequently limited by the interval between two adjacent pulses of a pulse generator sensing the velocity. In case the velocity varies within a great range, differently long periods are available for the calculating operations. Velocities that are varying within great ranges occur, for instance, with vehicle wheels. In vehicles incorporating anti-skid control devices, the rotational speeds are monitored by sensors associated with the wheels. In a device for preventing a wheel lock when braking that is known from the British Application No. 2,052,902, a sensor arranged on the drive shaft is connected via pulse-former circuits to input circuits which are connected with the bus of a microprocessor. In addition, memories and counters are connected to the bus. This bus comprises a data bus, an address bus and a control bus. In between two adjacent pulses of the sensor, the clock pulses of a clock generator are summed up in the counters. The rates of counted values which occurred in several pulse periods are stored in a series of registers from which they are called off by the microprocessor for the speed calculation. With each pulse of the sensor, an interrupt is demanded from the microprocessor. This interrupt will commence the speed calculation only when the calculating period required is shorter than the pulse period. However, if the pulse period is shorter than a predetermined period that is commensurate with the calculating period, the interrupt signal will be rendered inoperative by masking until the calculating action has been completed. Only the subsequent interrupt signals will cause a new speed calculation.